1. Field of the Invention
The present invention relates to systems and methods for automatically controlling cranes in moving loads from a source location to a destination location. More specifically, the invention relates to systems and methods of automatically controlling cranes to move such loads according to paths learned from experienced human operators.
2. Related Art
Systems and methods for movement of loads by cranes are known in the art. However, in cranes utilizing wire ropes to suspend a load, it has long been a problem that the load tends to sway near the end of the load's path. This sway requires the crane operator to wait before lowering the load to its final destination, or to incorporate complicated and coordinated control motions to reduce the amount of sway. This waiting period proves costly when repeated over a number of loads.
Typically, crane operators have reduced sway of the load through complicated and coordinated movement of trolley and hoist control sticks. Over time, and with the proper training and experience, control stick movement may become a subconscious effort. However, less experienced operators find it more difficult to efficiently, quickly and safely move the load with less sway. Further, even experienced operators find such movement difficult at the end of extended periods of crane operation, due to growing fatigue. Moreover, such problems as fog or poor depth perception can cause operation of the crane to be slow, inefficient, or unsafe.
It is therefore desirable to provide a system which allows all crane operators to quickly, safely and efficiently move a load from a source location to a destination location.
Many known systems include physical mechanisms for absorbing the oscillatory energy of the load, thereby reducing the magnitude and duration of the load's sway. However, this approach involves reduction of sway induced by the operator's control of the crane, and not with preventing sway in the first place.
Various other systems are known for improving certain aspects of the unloading process. With the advent of reliable, affordable and physically small digital electronic computers, monitoring and/or control of the crane during the movement of loads has become possible.
For example, U.S. Pat. No. 3,517,830 (Virkkala) discloses compensation for operator-induced changes in acceleration. U.S. Pat. No. 4,037,742 (Gustafsson) dislcosed program-controlled loading. U.S. Pat. No. 4,504,918 (Axmann) discloses collision avoidance during a ship loading process by automatically switching off and stopping the crane. U.S. Pat. No. 4,516,117 (Couture et al.) discloses a sensing of a position of a load, and activating an alarm when a potentially dangerous detected physical location is encountered. U.S. Pat. Nos. 4,717,029 (Yasunobu et al.) and U.S. Pat. No. 4,756,432 (Kawashima et al.) disclose use of a velocity profile in an unloading process. U.S. Pat. No. 4,815,614 (Putkonen et al.) discloses definition of a maximum speed based on a measured weight of a load. U.S. Pat. No. 4,905,848 (Skjonberg) discloses use of a computer in which plural hoists are used on a single load. U.S. Pat. No. 2,988,237 (Devol) discloses an early system for programmed movement of articles. All documents cited in this specification are incorporated by reference herein as if reproduced in full below.
Man of the above systems involve complex theoretical considerations which are not readily adapted to a given load movement scenario. For example, a system for moving articles from a palette to a conveyer belt in a factory is not readily adapted to unloading containers from a ship's hold to a pier.
Moreover, many known systems generally do not involve an optimum allocation of control between a human operator and the computer. There are times when operator intervention should preferably be excluded, times when operator intervention is demanded, and still other times when it is preferably left to the operator whether to manually or automatically control the movement of the load.
Further, many known systems involve concentration on a small part of the load movement process, not on the overall "bottom line" efficiency of each unloading process and a series of many unloading processes. From an economic point of view, the long-term cost-effectiveness of a crane control system is determined by the frequency of load operations, with reduction of load sway and personal safety being among the considerations. This frequency is related to optimized allocation of automated and manual control of the crane during the load movement process.
Finally, the disclosed systems do not adequately use the expertise which is developed in human operators over long periods of time and in a variety of load movement scenarios. Nor do the known systems repeatably apply this level of learned expertise to a variety of load types and load movement paths.
The present invention provides an economic and efficient solution to these shortcomings of known systems.